In accordance with the teachings of the present invention, an RF/ID interrogator is provided for recovering a data signal from an RF/ID tag. The interrogator includes a radio having a receiver portion to receive in-phase (I) and quadrature-phase (Q) signals from the RF/ID transponder transmitted at a predetermined bit-rate, and a processor coupled to the radio for controlling operation of the radio in accordance with stored program instructions.
In one embodiment of the invention, the interrogator performs over-sampling of the data signal received from the RF/ID tag in order to provide a high data recovery rate. The processor controls the over-sampling of the I and Q signals at a sampling rate higher than the transmitted bit-rate of the I and Q signals to provide plural signal samples that are stored in a buffer memory. The relative polarity of successive ones of the plural signal samples are compared by the processor. Based on this comparison, data bits are derived from the successive ones of the plural signal samples in correspondence with the number of the successive ones of the plural signal samples having same relative polarity. More specifically, the processor determines whether signal samples correspond to a xe2x80x9c1xe2x80x9d or a xe2x80x9c0xe2x80x9d based on the number on consecutive positive or negative signal samples. Thereafter, an encoded data signal may be recovered from the derived data bits.
In another embodiment of the invention, the interrogator performs a selection between the I and Q signals in order to achieve optimum data recovery. The processor detects a relative signal strength of the I and Q signals, and selects one of the I and Q signals for subsequent processing based on the detected relative signal strength. Data bits are then recovered from the selected one of the I and Q signals. The processor may select the one of the I and Q signals having highest initial signal strength, or having highest current signal strength. Alternatively, the processor may select a combination of the I and Q signals.
A more complete understanding of the RF/ID interrogator data recovery system will be afforded to those skilled in the art, as well as a realization of additional advantages and objects thereof, by a consideration of the following detailed description of the preferred embodiment. Reference will be made to the appended sheets of drawings, which Will first be described briefly.